Stabilizing muscles along the midsection are prone to develop when doing exercises like squats, deadlifts, and other exercises involving core stability.
As gamer2be has soapboxed, it's usually not going to be significant. But a single testimony can sometimes ingore a series of variables.
If you are truly concerned about maintaining a certain shoulder-to-waist ratio, I would recommend using a lifting belt or smith machine. The thick leather material of the lifting belt eases core stability, by re-distributing the load onto your hips. Smith machines have virtually no lateral movement, so the work needed to maintain stability is taken by the rails which the bar runs along.